The Rattleback is a cool physics gadget, that seems to defy the law of conservation of angular momentum...
The rattleback, also known as a celt or wobble stone, is a small top-shaped object witch has asymmetrical shape and peculiar behavior. When spun in one direction, it will often begin to wobble and then abruptly stop and reverse its spin.
The behavior of the rattleback top is due to its asymmetric shape, which causes it to have a preferred direction of rotation. If the top is spun in the preferred direction, it will spin smoothly and steadily. However, if it is spun in the opposite direction, any minor wobbling or deviation from a perfectly vertical axis of rotation will cause the top to tip over, and the friction with the surface will cause it to start spinning in the opposite direction.
This sudden reversal of direction is due to a combination of several factors, including the asymmetrical shape of the top, the way that the weight is distributed within the top, and the angle of the surface on which it is spinning. These factors all interact to create a complex system of forces that cause the rattleback to exhibit this unusual behavior.